December 2, 2013 — A University of Wyoming husband-and-wife research team was
part of a larger group that has made the first significant recovery of layered igneous
rocks from the Earth’s lowest ocean crust.

The discovery -- found in the “Hess Deep Rift” in the
Pacific Ocean -- confirms a long-held belief among geologists that such rocks
are a key part of the lower ocean crust formed at fast-spreading ridges.

Michael Cheadle, an associate professor, and Professor Barbara
John, both in UW’s Department of
Geology and Geophysics, are two co-writers (30 in all) of a research paper,
titled “Primitive Layered Gabbros from Fast-Spreading Lower Oceanic Crust,” published in the new issue of Nature. Nature is an
international weekly journal of science that publishes the finest peer-reviewed
research in all fields of science and technology.

The two were part of a 26-member international research team
that sailed to the Hess Deep, a deep scar in the Pacific Ocean’s sea floor,
between December 2012 and January 2013. Their mission was to study rocks
sampled about 3-4 kilometers below the sea floor in an effort to better
understand how the Earth’s crust is formed.

“To me, the key thing for the public is that, for the first
time ever, we recovered rocks from the lower-most part of the ocean’s crust.
This hasn’t been accomplished before,” Cheadle says. “For 50 years, people have
tried to drill to this depth or deeper, but have been unsuccessful.”

“The rocks were in situ, or in place,” John adds. “This is
not rock exposed at the surface because the tectonic plates collided and formed
mountains, but were recovered beneath the sea floor where they were formed.”

The world’s oceanic crust -- which makes up 70 percent of
the Earth’s surface -- is formed at mid-ocean ridges. At these ridges,
volcanoes sit above magma chambers, much like volcanoes one would see in
Hawaii, John says. These magma chambers are fed from below by the melting
mantle. Oceanic crust is made when this magma freezes.

“What we were drilling was the frozen remains of what once
was a magma chamber,” Cheadle says.

The cruise was part of the
Integrated Ocean Drilling Program (IODP), a multinational research
project that operates up to three research vessels that sail the world’s
oceans. The ships drill bore holes to collect samples of rock and sediment from
below the sea floor to address questions about geology, climate, oceanography
and natural hazards, including earthquakes. The U.S., Japan, Europe and several
other countries were involved in the 50-day, multimillion-dollar operation, funded,
in part, by the U.S. National Science Foundation’s (NSF) Division of Ocean Sciences.

During their voyage, Cheadle and John studied the geology of
the recovered core samples. They measured rock fractures and faults, and
examined the crystals that made up the rock.

And they found something that really surprised them.
Crystals of olivine, a common mineral in ocean crust, had a tree-like branch pattern
on the core samples. Cheadle used the
term “skeletal” and likened its growth to ice crystals on a car windshield. John
described it as similar to the ice that forms on a frozen puddle: large
crystals with a delicate branching structure, unlike any seen before in the
lower crust.

Because the rocks were found 3-4 kilometers (1.8-2.5 miles) beneath
the ocean floor, the rocks should have cooled much more slowly and not left
such a dramatic pattern, the two say.

“There’s something going on there that we don’t understand,”
John says.

During their research expedition, Cheadle and John, like the
other researchers aboard, took turns communicating to classrooms around the
globe via Skype.

“We’d tell a little story of what we were working on,” says
John, who mentioned speaking to a group of middle school students from France.
“They had excellent questions asked in English -- something I wish our system
could do better with here in the United States.”

Cheadle conversed with Craig Grimes, a professor of geology
at Ohio University, and his students. Grimes is a former UW doctoral student whom Cheadle and John supervised
during 2007.

Photo:Michael Cheadle, a UW associate professor of geology and
geophysics, examines rocks from the lower ocean crust of the Pacific Ocean with
Yumiko Harigane, a researcher from the National Institute of Advanced
Industrial Science and Technology in Japan. (Susan Gebbels Photo)